The invention relates to a process for the preparation of dodecahaloneopentasilanes from perhalopolysilanes in the presence of catalysts and a high-boiling solvent.
The silicon-hydrogen compounds obtainable from the dodecahaloneopentasilanes (neopentasilanes=tetrakis(silyl)silanes) are used for the deposition of Si—C in CVD processes.
The preparation of dodecahaloneopentasilanes is described, for example, in WO 20080513284 and J. Inorg. Nucl. Chem., 1964, Vol. 26, 421-425.
In WO 20080513284, hexahalodisilane is reacted with tertiary amines as catalysts to give mixtures containing tetrakis(trihalosilyl)silane. For working-up, the reaction mixture is evaporated to dryness in vacuo so that sparingly volatile impurities (e.g. perhalopolysilanes) cannot be separated off at all or can be separated off only incompletely. Purification is effected only after exchange of the chlorine atoms for hydrogen by distillation of the target product neopentasilane. Since alkylaluminium hydrides are used for this subsequent reaction, halogen-containing by-products account for an unnecessarily high consumption of these expensive starting compounds and are therefore an economic disadvantage.
J. Inorg. Nucl. Chem., 1964, Vol. 26, 421-425, discloses the preparation of dodecachloroneopentasilane from hexachlorodisilane or octachlorotrisilane with trimethylamine.
Furthermore, it is stated there that dodecachloroneopentasilane forms adducts with the tetrachlorosilane formed as a by-product. Only by expensive and tedious drying of the solid in vacuo is it possible to remove the tetrahalosilane, bound in the crystal, and other volatile impurities, such as, for example, hexachlorodisilane. The process is therefore unsuitable for the preparation of the pure perhalopolysilanes on an industrial scale.
An object was the development of a process which no longer has the disadvantages of the prior art.